1. Field of Invention
This invention relates to an apparatus for measuring the remaining weight of fuel in a fuel tank on a flying object; and more particularly, to such an apparatus wherein transducers are utilized to provide information which is processed by a processor to generate a signal relating to the weight.
2. Description of Prior Art
A known apparatus for measuring the remaining weight of fuel in a fuel tank on a flying object, such as described in U.S. Pat. No. 4,281,542, comprises a plurality of electrostatic capacity type liquid level gauges, wherein the electrostatic capacity which is outputted by each level gauge is proportional to the level of fuel and its electrostatic coefficient.
FIG. 1 is a block diagram depicting a known apparatus, comprising a plurality of electrostatic capacity type transducers, which act as the liquid level gauges 3, disposed in a fuel tank 1, provided on a flying object, e.g. in a main wing of an aircraft, for holding fuel 2. The plurality of gauges 3 are distributed over the entire inside area of the fuel tank 1, as depicted, for the purposes of measuring the levels .delta..sub.l. . . .delta..sub.n of fuel at various parts of fuel tank 1. A compensator unit 4 is provided for compensating the electrostatic coefficient K of fuel 2. A density meter 5 is provided for measuring the density .rho. of fuel 2. A processor unit 6 is suitably configured for fuel tank 1 and comprises a memory 7, for storing information including the fuel level (l)--volume (V) characteristic shown in FIG. 2, and the values as measured; an electrostatic capacity input interface 8, which is connected to gauges 3 and compensator unit 4; a frequency input interface 9, which is connected to density meter 5; an input/output interface 10 to which values, such as the total weight of the flying object and the weight of the fuel to be supplied, are inputted, and from which the results of calculation by calculation function unit 12, are outputted; and calculation function unit 12 which receives data and inputted values from memory 7 through a data bus 11, and performs the necessary calculations based on such data and values. Units 7,8,9,10,12 are connected to data bus 11 as depicted.
Electrostatic capacity input interface 8 receives the output of level gauges 3 (electrostatic capacity values Q.sub.l to Q.sub.n) which are proportional to levels .delta..sub.l. . . .tbd..sub.n of fuel 2, respectively, at various points in fuel tank 1, and the output of compensator unit 4 for correcting electrostatic coefficient K of fuel 2. The calculation function unit 12 calculates corrected fuel levels l.sub.11. . . l.sub.n1 by correcting the effect of the electrostatic coefficient K of the on the electrostatic capacity values Q.sub.l to Q.sub.n, respectively, the volume V corresponding to the corrected fuel levels l.sub.l1. . . l.sub.n1, respectively, in accordance with the fuel level-volume characteristic adapted for the shape of the fuel tank 1 and stored in memory 7.
If the flying object has tilted (e.g. rolled), the height H of immersion and the angle .alpha. of inclination of the fuel surface are calculated from the values detected by, for example, two of level gauges 3. A curve showing the fuel level-angle-volume characteristic is priorly obtained from the angle .alpha. and the fuel level-volume characteristics and entered into the memory 7. This curve has a shape depending on the shape of the fuel tank and shows the relationship between the level l of fuel above a particular point of the bottom of a particular fuel tank, the angle .alpha. of inclination and the volume V of the fuel. The volume V is obtained by calculation function unit 12 from the curve and multiplied by the density .rho., as measured by the density meter 5, whereby the remaining weight W of the fuel is determined by the equation W=.rho..times.V.
The apparatus has many deficiencies and disadvantages, such as, for example, since the known apparatus requires a plurality of electrostatic capacity type level gauges, a plurality of coaxial cable or shielded wires are needed for connecting the processor to the individual electrostatic devices. Disadvantageously, such coaxial cables or shielded wires are expensive, and are of substantial weight, especially, where the fuel tanks are a distance from the processor, the weight may be considerable. Furthermore, the electrostatic devices have low resistance to vibration and are moreover difficult to repair and maintain.
Thus, in the art, there is a need for a simpler, accurate and reliable and also more inexpensive, apparatus for measuring the weight of fuel remaining in a tank on a flying object.